This invention concerns improvements in diffusion foggers used in photographic, motion picture, video production, and entertainment industries.
Smoke effect in the film industry can be broken down into two main categories: (1) SMOKE and (2) FOG or "atmosphere". SMOKE is generally a very thick, milky cloud of true smoke: the result of a volatile oil or other fuel being heated to just below its flash point. A list of SMOKE making equipment would include Igebas.TM., Mole Guns.TM., and Roscoes.TM., all of which involve some form of heating element. FOG, or "atmosphere", is a more common albeit somewhat less dramatic effect, helping to soften images, enhance light beams, and give the impression of dust or moisture, among other things. In the early days of cinema, smoke making equipment was used to create indoor fog effects. It was all they had, and one could achieve a nice effect simply by thoroughly mixing the smoke with the air, thinning it into a haze. The one problem, aside from the danger of fire, was the tendency for crew members to fall over dead from breathing the smoke. Mixed with a bit of poison, the smoke from these devices made a terrific insecticide, which was its original function before the turn of the century.
In 1955, the oil cracker barrel was designed to create a fog effect without combustion in the following way. Compressed air is shot into a bath of oil from submerged nozzles, bubbling violently up through the barrel and sending a steady, thick cloud of oil particles, looking very much like a cloud of water vapor, into the air. Large, heavy particles fall quickly out of the cloud, while smaller particles stay aloft for up to several hours. Oil particles smaller than a certain critical diameter remain in the air essentially forever, buoyed by the brownian motion of air molecules.
With a cracker barrel, all sizes of droplets are produced and sent into the air, only a small fraction of which are small enough to hang in the air for more than an hour. The rest of the oil falls out and forms a residue on food, expensive camera equipment, and in the lungs of nearby crew members. The "smoke", though relatively safe to breathe, is uncomfortable in the lungs. It burns the throat and can cause nausea and dizziness after only a few hours of moderate exposure Yet the cracker barrel has remained a very popular smoke machine for almost 30 years because it is cheap and simple to run, can create a range of effects from subtle haze to thick fog, and although it does cause discomfort it is a definite health improvement over heating element-based smoke systems.
In 1986, Reel Efx Inc. introduced the Diffusion Fogger to the marketplace. The Diffusion Fogger, now known as the Senior Diffusion Fogger, was a vast improvement over the cracker barrel, primarily because of the size of oil particles produced. The Senior Diffusion Fogger sends only the smallest particles, those at or below the critical diameter mentioned above, into the air, and lots of them, producing an almost identical effect for longer periods without residue or discomfort to the film crew.
The Food and Drug Administration designation CFR 21.878 defines the purity of the food grade oil used by the Diffusion Fogger. Specifically, it does not allow the presence of polycyclic aromatic hydrocarbons (PAH) or trace heavy metals, both of which may be found in mineral oil used industrially or in systems employed by the special effects industry. PAH's are known to be carcinogenic at very low levels, and the toxicological effects of heavy metals are well established medically in a variety of pathologies.
The Senior Diffusion Fogger produces "smoke" using compressed air and a highly purified version of the oil found in a cracker barrel, but there the similarities stop. Instead of simply bubbling the air up through the oil, the Diffusion Fogger atomizes it in rather the same way that modern snowmaking equipment atomizes water. A special nozzle draws oil to its intake and mixes it with high pressure air, firing a very fine mist of oil and air directly into a filtration chamber. The chamber is filled with small nylon balls, around which the suspended oil particles are forced to travel for several inches. Larger, more massive particles, which cannot negotiate the sharp turns within the chamber, strike these obstacles, form droplets, and trickle back down into the oil tank to be recycled. As a final step, the smoke is then sent through a fibrous material which smoothes the flow and filters out any large particles which managed to make it through the grueling course laid out by the packed nylon balls.
An analogous situation occurs within the human lung. As it is inhaled, air is forced to turn sharply and flow through tight passages, while cilia along the walls of bronchial tubes catch any foreign particles that lumber into them. By definition, the Diffusion Fogger's unique filtration system releases into the air only those particles which can evade cilia indefinitely, going out as easily as they went in and saving the lungs a lot of aggravation. Indeed, despite the higher cost, the Diffusion Fogger became popular during the first two years of its availability. Despite the popularity, problems remained in that size and weight and power requirements added a burden to shipment, installation and use.